Endocrine Mechanisms Regulating Post-Diapause Development in the Cabbage Armyworm, Mamestra brassicae

Abstract

Diapause, a programmed developmental arrest at a specific stage, is common in insects and is regulated by hormones. It is well established that in pupal diapause, cessation of ecdysteroid secretion from the prothoracic glands (PGs) after pupal ecdysis leads to diapause initiation, while resumption of its secretion induces post-diapause development. However, what regulates the activity of the glands is poorly understood, especially for the glands of diapause-terminated pupae. In the present study, we investigate the mechanisms by which post-diapause development is regulated in the cabbage armyworm Mamestra brassicae. We demonstrate that the brain is necessary for the initiation of post-diapause development and that the factor in the brain responsible for the activation of the PGs is the prothoracicotropic hormone (PTTH). Further, through measuring the hemolymph PTTH titers by time-resolved fluoroimmunoassay, we show that PTTH is actually released into the hemolymph prior to the activation of the PGs. Although its peak titer is much lower than expected, this low concentration of PTTH is most likely still effective to activate the PGs of post-diapause pupae, because the responsiveness to PTTH of the glands at this stage is very high compared to that of nondiapause pupal PGs. These results strongly suggest that in M. brassicae, PTTH serves as a trigger to initiate pupa-adult development after diapause termination by stimulating the PGs to secrete ecdysteroid.

Identification of ecdysteroidogenic enzyme genes and their expression during pupal diapause in the cabbage armyworm, Mamestra brassicae

“…In the present study, during the postdiapause quiescence phase, gene expression levels of ecdysteroidogenic enzymes increased, although the fold change differed amongst enzymes. In M. brassicae pupae, ecdysteroidogenesis was recovered in PGs during the postdiapause quiescence phase; additionally, ecdysone and 20E are known to be necessary for postdiapause development of M. brassicae (Yamada et al, ). Increased expression of ecdysteroidogenic enzyme genes in the PGs might enable enough ecdysteroid to be synthesized for postdiapause pupal development.…”

“…) according to Yamada et al . (). To prepare ND pupae, larvae were reared at 25 °C under a 14‐h light/10‐h dark cycle.…”

“…M. brassicae shows aestival and winter diapause in the pupal stage, and winter diapause can be induced by rearing under conditions of short‐day length and low temperature throughout larval stages. Diapause is terminated by long‐term chilling and postdiapause development is initiated by warming (Yamada et al ., ). Although diapause initiation and termination are easily induced in M. brassicae , ecdysteroidogenic enzyme genes have not been reported.…”

Myosuppressin is involved in the regulation of pupal diapause in the cabbage army moth Mamestra brassicae

“…It is also interesting to speculate about the role of MS in the maintenance and termination of diapause. In our previous study, we demonstrated that PTTH secretion and consequent PG activation is necessary for the initiation of post-diapause development 29 . We expect MS secretion level to be relatively high during diapause but low after diapause termination.…”

“…Anti-BMS mouse monoclonal antibody was produced in our laboratory 17 . Anti-ecdysone antiserum was the same as that used in our previous studies 12 29 . Horseradish peroxidase-labeled anti-rabbit IgG antibody, Alexa Fluor 488-labeled goat anti-mouse IgG antibody, and biotin-labeled anti-rabbit IgG antibody were purchased from Thermo Fisher Scientific, Life Technologies and Amersham Biosciences, respectively.…”